class Singleton:
    _instance = None
    
    @classmethod
    def get_instance(cls):
        if cls._instance is None:
            cls._instance = cls()
        return cls._instance
    
class Service:
    def __init__(self):
        self._result = None
    
    def run(self):
        pass
    
    def get_result(self):
        return self._result